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Holmium is a chemical element; it has symbol Ho and atomic number 67. It is a rare-earth element and the eleventh member of the lanthanide series. It is a relatively soft, silvery, fairly corrosion-resistant and malleable metal. Like many other lanthanides, holmium is too reactive to be found in native form, as pure holmium slowly forms a yellowish oxide coating when exposed to air. When isolated, holmium is relatively stable in dry air at room temperature. However, it reacts with water and corrodes readily, and also burns in air when heated.
In nature, holmium occurs together with the other rare-earth metals (like thulium). It is a relatively rare lanthanide, making up 1.4 parts per million of the Earth's crust, an abundance similar to tungsten. Holmium was discovered through isolation by Swedish chemist Per Theodor Cleve. It was also independently discovered by Jacques-Louis Soret and Marc Delafontaine, who together observed it Spectroscopy in 1878. Its oxide was first isolated from rare-earth ores by Cleve in 1878. The element's name comes from Holmia, the Latin name for the city of Stockholm.
Like many other lanthanides, holmium is found in the minerals monazite and gadolinite and is usually commercially extracted from monazite using ion-exchange techniques. Its compounds in nature and in nearly all of its laboratory chemistry are trivalently oxidized, containing Ho(III) ions. Trivalent holmium ions have fluorescent properties similar to many other rare-earth ions (while yielding their own set of unique emission light lines), and thus are used in the same way as some other rare earths in certain laser and glass-colorant applications.
Holmium has the highest magnetic permeability and magnetic saturation of any element and is thus used for the of the strongest static . Because holmium strongly absorbs neutrons, it is also used as a burnable poison in nuclear reactors.
Holmium, like all of the lanthanides, is paramagnetic at standard temperature and pressure. However, holmium is ferromagnetic at temperatures below . It has the highest magnetic moment () of any naturally occurring element and possesses other unusual magnetic properties. When combined with yttrium, it forms highly magnetism compounds.
It is a relatively soft and Ductility element that is fairly corrosion-resistant and chemically stable in dry air at standard temperature and pressure. In moist air and at higher temperatures, however, it quickly oxidation, forming a yellowish oxide. In pure form, holmium possesses a metallic, bright silvery luster.
Holmium is quite electropositive: on the Pauling electronegativity scale, it has an electronegativity of 1.23. It is generally trivalent. It reacts slowly with cold water and quickly with hot water to form holmium(III) hydroxide:
Holmium metal reacts with all the stable :
Holmium dissolves readily in dilute sulfuric acid to form solutions containing the yellow Ho(III) ions, which exist as a Ho(OH2)93+ complexes:
The known isotopes of holmium range from 140Ho to 175Ho. The primary decay mode before the stable isotope 165Ho, is beta plus decay to dysprosium isotopes, and the primary mode after is beta minus decay to erbium isotopes. Of the 35 synthetic radioactive isotopes among these, the most stable one is holmium-163 (163Ho), with a half-life of 4570 years. The next most stable is holmium-166 (166Ho) having a half-life of 26.812 hours, and others have half-lives under 4 hours.
The nuclear isomer 166m1Ho has the unusually long half-life of 1133 years. With a very low excitation energy, it does not decay to the ground state but beta-decays directly, having a particularly rich spectrum of , making this isotope useful as a means for Calibration gamma ray spectrometers.
Holmium-166 (ground state) has been studied for medical application.
Other are known for holmium. Holmium(III) sulfide has orange-yellow in the monoclinic crystal system, with the space group P21/ m (No. 11). (2025). 9783540649663, Springer. ISBN 9783540649663 Under high pressure, holmium(III) sulfide can form in the cubic and orthorhombic . It can be obtained by the reaction of holmium(III) oxide and hydrogen sulfide at . Holmium(III) selenide is also known. It is antiferromagnetic below 6 K.
In addition, holmium(III) iodide can be obtained by the direct reaction of holmium and mercury(II) iodide, then removing the mercury by distillation.
The Swedish chemist Per Teodor Cleve also independently discovered the element while he was working on erbia earth (erbium oxide). He was the first to isolate impure oxide of the new element. Using the method developed by the Swedish chemist Carl Gustaf Mosander, Cleve first removed all of the known contaminants from erbia. The result of that effort was two new materials, one brown and one green. He named the brown substance holmia (after the Latin name for Cleve's home town, Stockholm) and the green one thulia. Holmia was later found to be the holmium oxide, and thulia was thulium oxide. The pure oxide was only isolated in 1911 and the metal in 1939 by Heinrich Bommer.
In the English physicist Henry Moseley's classic paper on , holmium was assigned the value 66. The holmium preparation he had been given to investigate had been impure, dominated by neighboring dysprosium. He would have seen x-ray emission lines for both elements, but assumed that the dominant ones belonged to holmium, instead of the dysprosium impurity.
Holmium makes up 1.3 parts per million of the Earth's crust by mass.ABUNDANCE OF ELEMENTS IN THE EARTH'S CRUST AND IN THE SEA, CRC Handbook of Chemistry and Physics, 97th edition (2016–2017), p. 14-17 Holmium makes up 1 part per million of the , 400 parts per quadrillion of seawater, and almost none of Earth's atmosphere, which is very rare for a lanthanide. It makes up 500 parts per trillion of the universe by mass.
Holmium is commercially extracted by ion exchange from monazite sand (0.05% holmium), but is still difficult to separate from other rare earths. The element has been isolated through the redox of its anhydrous chloride or fluoride with metallic calcium. Its estimated abundance in the Earth's crust is 1.3 mg/kg. Holmium obeys the Oddo–Harkins rule: as an odd-numbered element, it is less abundant than both dysprosium and erbium. However, it is the most abundant of the odd-numbered heavy lanthanides. Of the lanthanides, only promethium, thulium, lutetium and terbium are less abundant on Earth. The principal current source are some of the ion-adsorption clays of southern China. Some of these have a rare-earth composition similar to that found in xenotime or gadolinite. Yttrium makes up about two-thirds of the total by mass; holmium is around 1.5%. Holmium is relatively inexpensive for a rare-earth metal with the price about 1000 USD/kg.
Holmium is used to create the strongest artificially generated , when placed within high-strength magnets as a magnetic pole piece (also called a magnetic flux concentrator). Holmium is also used in the manufacture of some .
Holmium can act as a sensitizer in sodium yttrium fluoride which takes advantage of its absorption in the NIR-II window. Holmium allows for lanthanide nanomaterials to have tunable emission and excitation in the NIR-II. Under 1143 nm excitation the interfacial energy transfer to other lanthanides allows a redshift in emission for biological applications. This allows deeper penetration than typically used 980 nm and 808 nm lasers.
Holmium-doped yttrium iron garnet (YIG) and yttrium lithium fluoride have applications in solid-state lasers, and Ho-YIG has applications in and in microwave equipment (e.g., ). Holmium lasers emit at 2.1 micrometres. They are used in medical, dental, and optical fiber applications. It is also used in the enucleation of the prostate.
Since holmium can absorb nuclear fission-bred neutrons, it is used as a burnable poison to regulate nuclear reactors. It is used as a Colourant for cubic zirconia, providing pink coloring, and for glass, providing yellow-orange coloring. In March 2017, IBM announced that they had developed a technique to store one bit of data on a single holmium atom set on a bed of magnesium oxide. With sufficient quantum and classical control techniques, holmium may be a good candidate to make quantum computers.
Holmium is used in the medical field, particularly in laser surgery for procedures such as kidney stone removal and prostate treatment, due to its precision and minimal tissue damage. Its isotope, holmium-166, is applied in targeted cancer therapies, especially for liver cancer, and it also enhances MRI imaging as a contrast agent.
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